1. Field of the Invention
This invention relates to a guide roller assembly for use in a vacuum sizing tank that cools molten plastic extrudate as it leaves the extruder in order to hold the size and shape of the extrudate as the molten plastic cools and hardens. The vacuum sizing tank contains water through which the extrudate passes as it cools. The guide roller assembly guides the extrudate and maintains it in a straight line below the surface of the water within the vacuum sizing tank. The guide roller assembly permits movement of the guide rollers from a working position where the guide rollers guide and hold down the extrudate to a nonworking position where the guide rollers do not interfere with the initial stringing of the extrudate through the vacuum sizing tank.
2. Description of the Prior Art
Efforts have been made in the plastics industry to provide for the controlled cooling and accurate sizing of molten plastic extrudate after it leaves the plastic extruder. The extrudate can easily be deformed if excessive pressure is applied to the outer surface of the extrudate. To prevent this type of deformation, vacuuming cooling and sizing tanks have been developed that have a water bath within a vacuum chamber which prevents excessive pressure from being applied to the surface of the extrudate as it cools. An example of such an arrangement is found in U.S. Pat. No. 5,340,295 entitled "Vacuum Sizing Apparatus With Controlled Vacuum".
When very small diameter tubing or other small extrudate is cooled in a vacuum chamber, it is essential to keep the extrudate under water even though the extrudate may have a tendency to float to the surface of the water, and it is further essential to keep the extrudate in a relative straight line as it moves from one end of the cooling tank to the other. An example of such a vacuum tank for small diameter extrudate may be found in U.S. patent application Ser. No. 08/298,325 filed Aug. 30, 1994 and entitled "Vacuum Tank For Vacuum Sizing Apparatus".
In earlier vacuum sizing tanks, guide rollers have been positioned sporadically through the tank to hold down the extrudate and guide it through the vacuum sizing tank. It has been difficult to thread the extrudate under the rollers in present vacuum sizing tanks and it has been difficult to align the rollers to precisely guide the extrudate in straight line through the tank.